Cooking oils, such as those used in commercial or institutional deep fryers, tend to become contaminated with things such as moisture and carbonized food particles during frying. Also, the oils also tend to break down chemically after extended use, often causing the oil to foam or smoke or to exhibit an unpleasant odor, poor appearance, or unsatisfactory taste. It has been found that keeping the cooking oil clean by filtering it on a regular basis to remove the particulate matter tends to extend the useful life of the cooking oil and increase the quality and appearance of foods cooked in the oil.
Accordingly, a variety of specialized systems and filter media for filtering cooking oil have been developed. In one widely used type of filtration system, contaminated oil is transferred from the deep fryer to an oil filtering pan. The oil is caused to flow through a filter and then drained out of the filtering pan and returned to the deep fryer. Two of the most commonly used filtering media are filter pads and filter paper. As compared to filter pads, filter paper is relatively thin and tends to remove particulate matter less effectively and to have a shorter useful life. Nonetheless, it has been observed that within the same facility, while some personnel prefer to use filter pads, others prefer to use filter paper. Thus, a filtration system ideally should be amenable to use with both filter pads and filter paper.
A problem with existing filtration systems is that either: (1) they are able to be used with only a single filter media, that is, either filter pads or filter paper, but not both; or (2) although usable with both filter pads and filter paper, less effective filtering is achieved because only a "non-positive" seal is obtained. As to this second point, it has been found that when a non-positive seal is formed, there is a tendency for some oil to flow around the filter rather than through the filter, thereby allowing unfiltered contaminated oil to be returned to the deep fryer. An example of an oil filtering pan which provides only a non-positive seal is discussed directly below.
It is known to secure a filter, whether pad or paper, within an oil filtering pan by placing a weight ring on top of the filter to compress the filter around the periphery thereof to form a seal. The seal is sometimes unsatisfactory in that oil is permitted to flow around the filter rather than through the filter, thereby allowing unfiltered contaminated oil to be returned to the deep fryer. This flow of oil around the filter is believed to occur because only the weight of the weight ring itself is applied to the filter, thereby forming a "non-positive" seal. A configuration that yields a "positive" seal (i.e., that applies additional pressure other than by virtue of the weight of the member(s) overlying the filter, i.e., the weight ring) is desirable to more effectively prevent the flow of oil around, rather than through, the filter.
Another type of known oil filtering pan includes a support surface on which a filter is placed so as to overlie an opening in the bottom of the pan for the passage of filtered oil. A sealing ring is connected at one side of the support surface for pivotal movement between: (1) a sealing position in which the sealing ring compresses the filter against the support surface; and (2) an access position in which the sealing ring is swung outwardly away from the filter compartment so that a filter may be installed or removed. A disadvantage of this type of oil filtering pan is that it is usable only with filter pads since the configuration of the sealing ring does not allow for the use of filter paper. Specifically, the sealing ring is provided with a pair of arms, each carrying a horizontal pin. A pair of hinge members is provided adjacent one edge of the substantially rectangular filter compartment. Each hinge member has an opening therethrough for engagement of a corresponding one of the pins on the weight ring. The sealing position of the sealing ring is fixed because the distance between the filter support surface and the bottom of the sealing ring is constant. This filtering assembly is not amenable for use with filter paper because the sealing ring in its sealing position lies above the filter paper and is not capable of being positioned so as to compress the filter paper to form a seal.
In summary, there exists an oil filtering pan usable with both filter pads and filter paper. However, this pan achieves only a non-positive seal around the filter thereby providing less effective removal of particulate matter and allowing unfiltered contaminated oil to be returned to the deep flyer. Also, it is known to urge a sealing ring downwardly against a filter so as to create a positive seal around the filter. However, this type of filter holder assembly can accommodate only one type of filter media, i.e., filter pads.
A convenient oil filtering pan that is usable with both filter pads and filter paper and that provides more effective removal of particulate matter from contaminated oil is desirable.